Power supply circuit, high-frequency power amplification circuit, and power supply control method

ABSTRACT

A power supply circuit ( 10 ) includes: a linear amplifier ( 11 ) for generating a linear amplification signal based on an input signal; a first switching amplifier ( 12 ) for generating a first switching amplification signal of a first frequency band based on the linear amplification signal; a second switching amplifier ( 13 ) for generating a second switching amplification signal of a second frequency band based on the first switching amplification signal; and a power supply unit ( 14 ) for supplying a combined signal in which the linear amplification signal and the first and second switching amplification signals are combined to an external circuit as a power supply. It is therefore possible to improve the power efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2014/002464, filed on May 9, 2014, which claims priority fromJapanese Patent Application No. 2013217276, filed on Oct. 18, 2013, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a power supply circuit, ahigh-frequency power amplification circuit, and a power supply controlmethod, and more particularly, to a power supply circuit, ahigh-frequency power amplification circuit, and a power supply controlmethod that amplify an input signal and generate a power supply.

BACKGROUND ART

A modulation scheme used for radio communications such as a modernmobile phone and the like has a high-frequency utilization efficiencyand a high peak-to-average power ratio (PAPR). In order to amplify asignal to which an amplitude modulation is applied by using an AB classamplifier that has been conventionally used in a radio communicationfield, it is necessary to use an amplifier operating with sufficientback-off to maintain a linearity. Generally, the required back-off valueis at least approximately equal to a value of the PAPR. However, in theAB class amplifier, the maximum efficiency is obtained when it operatesat the saturation point and the efficiency of the amplifier decreaseswith increasing the back-off value. Therefore, it is difficult toimprove the power efficiency of the power amplifier for amplifying ahigh-frequency modulation signal having a high PAPR.

As a power amplifier for amplifying a modulation signal having a highPAPR with high efficiency, a polar modulation power amplifier is used.In the polar modulation power amplifier, the high-frequency modulationsignal used for radio communication is generated from polar coordinatecomponents of amplitude and phase. FIG. 9 shows an example of the polarmodulation power amplifier (high-frequency power amplification circuit)disclosed as related art in Non-Patent Literature 1.

The circuit shown in FIG. 9 includes a high-frequency modulation signalinput terminal 101, an amplitude signal input terminal 102, a powersupply circuit 103, a high-frequency power amplifier 104, and ahigh-frequency modulation signal output terminal 105. The power supplycircuit 103 further includes a linear amplifier 106, a subtractor 107, acurrent detection resistor 108, a hysteresis comparator 109, a switchingamplifier 110, an inductor 111, and a power supply terminal 112.

A harmonic modulation signal that is amplitude-modulated orphase-modulated is input to the high-frequency modulation signal inputterminal 101 and this harmonic modulation signal is transmitted to thehigh-frequency power amplifier 104. An amplitude signal in the harmonicmodulation signal input through the high-frequency modulation signalinput terminal 101 is input to the amplitude signal input terminal 102.The signal input through the amplitude signal input terminal 102 ishighly efficiently amplified by the power supply circuit 103 and issupplied from the power supply terminal 112 as a power supply of thehigh-frequency power amplifier 104. The high-frequency power amplifier104 amplifies the signal input through the high-frequency modulationsignal input terminal 101 and outputs the amplified signal to thehigh-frequency modulation signal output terminal 105.

The power supply circuit 103 has a configuration in which both theswitching amplifier 110 and the linear amplifier 106 are arranged so asto amplify the input signal in high efficiency and with low distortion.The amplitude signal input through the amplitude signal input terminal102 is input to the linear amplifier 106. The output impedance of thelinear amplifier 106 is low. The linear amplifier 106 linearly amplifiesthe input signal and outputs the amplified signal. The signal output bythe linear amplifier 106 is transmitted to the power supply terminal 112through the current detection resistor 108.

The subtractor 107 is connected to both ends of the current detectionresistor 108 and outputs a value obtained by subtracting a voltage ofthe power supply terminal 112 from a voltage of the output signal of thelinear amplifier 106. Here, because the input impedance of thesubtractor 107 is high, the subtractor 107 does not consume a largeamount of electric power supplied to the power supply terminal 112 andthe output signal of the linear amplifier 106. Further, because theimpedance of the current detection resistor 108 is set to low, thevoltage applied to both ends of the current detection resistor 108 isnegligibly small compared to the voltage applied to the power supplyterminal 112.

The subtractor 107 outputs the output signal, which is a subtractionresult, to the hysteresis comparator 109. The hysteresis comparator 109makes a sign determination of the input signal and outputs the result ofthe determination to the switching amplifier 110. However, thehysteresis comparator 109 has a function to hold the latest output stateand has a hysteresis width (V_hys), if the latest output state is “low”,the output state changes to “high” when the input signal level becomesequal to or greater than V_hys/2 and if the latest output state is“high”, the output state changes to “low” when the input signal levelbecomes equal to or smaller than −V_hys/2.

The switching amplifier 110 amplifies the signal input through thehysteresis comparator 109 and outputs the amplified signal to the powersupply terminal 112 via the inductor 111. In this case, the currentsupplied from the switching amplifier 110 via the inductor 111 and thecurrent supplied from the linear amplifier 106 via the current detectionresistor 108 are combined and the power is supplied from the powersupply terminal 112.

The above-mentioned power supply circuit 103 has two advantages: highlinearity of the linear amplifier 106 and high efficiency of theswitching amplifier 110. This is because in the power supply circuit103, the output voltage is determined by the linear amplifier 106 havinglow output impedance and most of the output current is supplied by theswitching amplifier 110 with high efficiency. The current output throughthe power supply terminal 112 is a sum of the output current of thelinear amplifier 106 and the output current of the switching amplifier110. A potential of the power supply terminal 112 is determined by thelinear amplifier 106 having low output impedance. In order to maintainthe electric potential of the power supply terminal 112 to a targetvalue, the current is supplied by the linear amplifier 106. The outputcurrent of the linear amplifier 106 is detected by using the currentdetection resistor 108 and the hysteresis comparator 109 and the currentsupplied by the switching amplifier 110 is adjusted so that the outputcurrent of the linear amplifier 106 is prevented from becomingexcessive.

By using the above-mentioned method, most of the current output throughthe power supply terminal 112 is supplied by the switching amplifier 110and the output current of the linear amplifier 106 can be used only forcorrection of an error component of the switching amplifier 110.

CITATION LIST Non Patent Literature

-   [Non-Patent Literature 1] Donald F. Kimbal, Jinho Jeong, Chin Hsia,    Paul Draxler, Sandro Lanfranco, Walter Nagy, Kevin Linthicum,    Lawrence E. Larson, Peter M. Asbeck, [High-Efficiency    Envelope-Tracking W-CDMA Base-Station Amplifier Using GaN HFETs],    IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 54, NO.    11, NOVEMBER 2006, pp. 3848-3856

SUMMARY OF INVENTION Technical Problem

However, the power supply circuit 103 disclosed in Non-Patent Literature1 has the following problem.

The problem of the power supply circuit 103 is that it is required tofurther improve the power efficiency thereof. That is, in the relatedart such as the power supply circuit 103, it is difficult to improve thepower efficiency thereof.

In order to increase the power efficiency of the power supply circuit103, it is required to reduce the output current of the linear amplifier106 whose power efficiency is low. In order to reduce the output currentof the linear amplifier 106, it is required to broaden the frequencybandwidth of the signal to be amplified by the switching amplifier 110in the power supply circuit 103. In order to broaden the frequencybandwidth of the signal to be amplified by the switching amplifier 110in the power supply circuit 103, it is required to shorten the switchingcycle of the switching amplifier 110. While the bandwidth of theswitching amplifier 110 is broadened when the switching cycle of theswitching amplifier 110 is shortened, the power efficiency of theswitching amplifier 110 is degraded. This is because the number of timesthat a through current or charging or discharging of a parasiticcapacitance generated when the level of the switching amplifier 110 isswitched between high and low occurs increases. Therefore, the actualpower efficiency of the power supply circuit 103 becomes maximum in aswitching cycle of the switching amplifier 110 and the power efficiencyof the power supply circuit 103 does not improve any more even when theswitching cycle becomes shorter or longer than this cycle.

The above problem becomes more serious as the bandwidth of the signal tobe amplified by the power supply circuit 103 becomes wider. This isbecause, in order to reduce the output current of the linear amplifier106, the bandwidth of the switching amplifier 110 needs to besufficiently wide with respect to the bandwidth of the signal to beamplified and the switching cycle needs to be shortened as the bandwidthof the signal to be amplified becomes wider.

In view of the aforementioned problem, the present invention aims toprovide a power supply circuit, a high-frequency power amplificationcircuit, and a power supply control method capable of improving a powerefficiency.

Solution to Problem

A power supply circuit according to the present invention includes: alinear amplifier for generating a linear amplification signal based onan input signal; a first switching amplifier for generating a firstswitching amplification signal of a first frequency band based on thelinear amplification signal; a second switching amplifier for generatinga second switching amplification signal of a second frequency band basedon the first switching amplification signal; and a power supply unit forsupplying a combined signal in which the linear amplification signal andthe first and second switching amplification signals are combined to anexternal circuit as a power supply.

A high-frequency power amplification circuit according to the presentinvention includes: a high-frequency power amplifier that amplifies ahigh-frequency modulation signal that is input; a linear amplifier forgenerating a linear amplification signal based on an amplitude signalwhich is an amplitude component of the high-frequency modulation signal;a first switching amplifier for generating a first switchingamplification signal of a first frequency band based on the linearamplification signal; a second switching amplifier for generating asecond switching amplification signal of a second frequency band basedon the first switching amplification signal; and a power supply unit forsupplying a combined signal obtained by combining the linearamplification signal and the first and second switching amplificationsignals to the high-frequency power amplifier as a power supply.

A power supply control method according to the present invention is apower supply control method in a power supply circuit, in which: thepower supply circuit generates a linear amplification signal based on aninput signal, the power supply circuit generates a first switchingamplification signal of a first frequency band based on the linearamplification signal, the power supply circuit generates a secondswitching amplification signal of a second frequency band based on thefirst switching amplification signal; and the power supply circuitsupplies a combined signal obtained by combining the linearamplification signal and the first and second switching amplificationsignals to an external circuit as a power supply.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a powersupply circuit, a high-frequency power amplification circuit, and apower supply control method capable of improving a power efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram for describing an outline ofa power supply circuit according to exemplary embodiments;

FIG. 2 is a block diagram showing a configuration of a power supplycircuit according to a first exemplary embodiment;

FIG. 3 is a block diagram showing a configuration of a high-frequencypower amplification circuit according to the first exemplary embodiment;

FIG. 4 is a block diagram showing a configuration of a power supplycircuit according to a second exemplary embodiment;

FIG. 5 is a block diagram showing a configuration of a power supplycircuit according to a third exemplary embodiment;

FIG. 6 is a block diagram showing an internal configuration of a pulsesignal generator used in the power supply circuit according to the thirdexemplary embodiment;

FIG. 7 is a block diagram showing an internal configuration of the pulsesignal generator used in the power supply circuit according to the thirdexemplary embodiment;

FIG. 8 is a block diagram showing an internal configuration of the pulsesignal generator used in the power supply circuit according to the thirdexemplary embodiment; and

FIG. 9 is a block diagram showing a configuration of a polar modulationpower amplifier disclosed in Non-Patent Literature 1.

DESCRIPTION OF EMBODIMENTS

(Outline of Exemplary Embodiments)

Prior to the description of exemplary embodiments, the outline of thecharacteristics of the exemplary embodiments will be described. FIG. 1is a schematic configuration of a power supply circuit according to theexemplary embodiments.

As shown in FIG. 1, a power supply circuit 10 according to the exemplaryembodiments includes a linear amplifier 11, a first switching amplifier12, a second switching amplifier 13, and a power supply unit 14. Thelinear amplifier 11 generates a linear amplification signal based on aninput signal. The first switching amplifier 12 generates a firstswitching amplification signal of a first frequency band based on thelinear amplification signal generated by the linear amplifier 11. Thesecond switching amplifier 13 generates a second switching amplificationsignal of a second frequency band based on the first switchingamplification signal generated by the first switching amplifier 12. Thepower supply unit 14 supplies a combined signal obtained by combiningthe linear amplification signal generated by the linear amplifier 11,the first switching amplification signal generated by the firstswitching amplifier 12, and the second switching amplification signalgenerated by the second switching amplifier 13 to an external circuit asa power supply.

As described above, the plurality of switching amplifiers amplifysignals in respective frequency bands, whereby it is possible to broadenthe frequency bandwidth of the switching amplifiers. It is thereforepossible to reduce the output current of the linear amplifier, wherebythe power efficiency of the power supply circuit can be improved.

(First Exemplary Embodiment)

In the following description, with reference to the drawings, a firstexemplary embodiment will be described. This exemplary embodiment showsan example in which two switching amplifiers are included in a powersupply circuit.

FIG. 2 is a block diagram showing a configuration example of a powersupply circuit 201 according to this exemplary embodiment. As shown inFIG. 2, the power supply circuit 201 according to this exemplaryembodiment includes a signal input terminal 202, a linear amplifier 203,a first current detector 204, a first hysteresis comparator 205, a firstswitching amplifier 206, a second current detector 207, a first low-passfilter 208, a second low-pass filter 209, a second hysteresis comparator210, a second switching amplifier 211, a third low-pass filter 212, anda signal output terminal 213.

The signal input terminal 202 receives a signal to be amplified (inputsignal). The linear amplifier 203 amplifies (linearly amplifies) thesignal input through the signal input terminal 202 and outputs theamplified signal (linear amplification signal) to the signal outputterminal 213.

The first current detector 204 detects a current value (currentcomponents) of the signal input to the signal output terminal 213 by thelinear amplifier 203 and outputs a signal (first detection signal)according to the current value that has been detected. For example, thefirst current detector 204 may be formed of the current detectionresistor 108 and the subtractor 107 as shown in FIG. 9 or may haveanother configuration as long as it can output a signal according to thedetected current (the same is applicable to the second current detector207).

The first hysteresis comparator 205 receives the output signal of thecurrent detector 204, determines whether the signal level of the inputsignal is high or low (positive/negative determination or leveldetermination), and outputs the determination result (firstdetermination signal). The first switching amplifier 206 receives theoutput of the first hysteresis comparator 205, amplifies(switching-amplifies) the received signal, and outputs the amplifiedsignal (first switching amplification signal). The first switchingamplifier 206 is formed of a non-inverting amplification circuit. Forexample, as one example of the non-inverting amplification circuit, thefirst switching amplifier 206 includes a buffer circuit 206 a thatinverts and amplifies the input signal and an inverter circuit(switching element) 206 b that is switched (ON/OFF) according to thesignal via the buffer circuit 206 a. The inverter circuit 206 b includestwo MOS transistors connected in series between a power supply 206 c andthe GND. The second switching amplifier 211 has a configuration similarto that of the first switching amplifier 206.

The first low-pass filter (output low-pass filter) 208 removeshigh-frequency components from the output signal of the first switchingamplifier 206 and outputs the resulting signal (first switchingamplification signal obtained by removing high-frequency components) tothe signal output terminal 213. The first current detector 204, thefirst hysteresis comparator 205, the first switching amplifier 206, andthe first low-pass filter 208 form a first switching amplifier thatgenerates the first switching amplification signal of the firstfrequency band.

The second current detector 207 detects current components from theoutput signal of the first switching amplifier 206 and outputs thedetection signal (second detection signal). The second low-pass filter(input low-pass filter) 209 removes high-frequency components from theoutput signal of the second current detector 207 and outputs theresulting signal. The second hysteresis comparator 210 receives theoutput signal of the second low-pass filter 209 (second detection signalafter the high-frequency components are removed) and outputs thedetermination signal (second determination signal) where the signallevel (high/low) has been determined. The second switching amplifier 211receives the output of the second hysteresis comparator 210 and outputsthe amplified (switching-amplified) signal (second switching signal).

The third low-pass filter (output low-pass filter) 212 removeshigh-frequency components from the output signal of the second switchingamplifier 211 and outputs the resulting signal (second switchingamplification signal after the high-frequency components are removed) tothe signal output terminal 213. The second current detector 207, thesecond low-pass filter 209, the second hysteresis comparator 210, thesecond switching amplifier 211, and the third low-pass filter 212 form asecond switching amplifier that generates the second switchingamplification signal of the second frequency band.

The signal output terminal (signal output unit) 213 outputs a combinedsignal obtained by combining the output signal of the linear amplifier203, the output signal of the first low-pass filter 208, and the outputsignal of the third low-pass filter 212. The signal output terminal 213forms a power supply unit that combines the linear amplification signaloutput from the linear amplifier 203, the first switching amplificationsignal output from the first low-pass filter 208, and the secondswitching amplification signal output from the third low-pass filter 212and supplies the combined signal to an external circuit as a powersupply.

The cutoff frequency of the first low-pass filter 208 is set to afrequency higher than the cutoff frequency of the third low-pass filter212 (the cutoff frequency of the third low-pass filter 212 is lower thanthe cutoff frequency of the first low-pass filter 208).

Further, the first hysteresis comparator 205 has a function to hold thelatest output state and has a hysteresis width (V_hys1). When the latestoutput signal is low, the output state changes to high when the voltageof the input signal becomes equal to or greater than V_hys1/2. Incontrast, if the latest output signal is high, the output state changesto low when the voltage of the input signal becomes equal to or lowerthan −V_hys1/2.

In a similar way, the second hysteresis comparator 210 has a function tohold the latest output state and has a hysteresis width (V_hys2). Whenthe latest output signal is low, the output state changes to high whenthe voltage of the input signal becomes equal to or greater thanV_hys2/2. In contrast, if the latest output signal is high, the outputstate changes to low when the voltage of the input signal becomes equalto or lower than −V_hys2/2.

The bandwidth of the signal amplified by the first switching amplifier206 is determined by the bandwidth of the first low-pass filter 208. Incontrast, the bandwidth of the signal amplified by the second switchingamplifier 211 is determined by the bandwidth in which the first low-passfilter 208, the second low-pass filter 209, and the third low-passfilter 212 are combined in series. Accordingly, with the configurationas stated above, a signal having a relatively high frequency isamplified by the first switching amplifier 206 (high-frequency amplifierin a first frequency band) and a signal having a low frequency isamplified by a second switching amplifier 211 (low-frequency amplifierin a second frequency band).

Since the frequency bands of the signals to be amplified by the firstswitching amplifier 206 and the second switching amplifier 211 aredifferent from each other, the two switching amplifiers are preferablyformed to have configurations specific for the respective bandwidths.For example, the first switching amplifier 206 may employ a device inwhich a parasitic capacitance is small (and an ON-resistance is large)to improve the efficiency of the first switching amplifier 206 when thefirst switching amplifier 206 is operated at a high speed and the secondswitching amplifier 211 may employ a device in which an ON-resistance issmall (and a parasitic capacitance is large) to improve the efficiencyof the second switching amplifier 211 when the second switchingamplifier 211 is operated at a low speed.

By separately using the switching amplifiers as stated above, the totalfrequency bandwidth of the first switching amplifier 206 and the secondswitching amplifier 211 can be broadened and the power loss can besuppressed. As a result, the output current of the linear amplifier 203can be reduced and the power efficiency of the whole power supplycircuit 201 is improved.

While the second current detector 207 is arranged between the firstswitching amplifier 206 and the first low-pass filter 208 in FIG. 2, thepositional relation between the second current detector 207 and thefirst low-pass filter 208 may be reversed. It is required, however, thatthe second current detector 207 be provided in a stage previous to thecircuit in which the output signal of the first low-pass filter 208 iscombined with the output signal of the linear amplifier 203 and theoutput signal of the third low-pass filter 212. The role of the secondcurrent detector 207 is to detect the current input to the signal outputterminal 213 by the first switching amplifier 206 via the first low-passfilter 208, and the second current detector 207 may have anyconfiguration as long as this role is fulfilled.

The second low-pass filter 209 is provided to make the frequency band inwhich the second hysteresis comparator 210 and the second switchingamplifier 211 are operated low by removing high-frequency componentsfrom the output of the second current detector 207. Therefore, thecutoff frequency of the second low-pass filter 209 is preferably madelower than the cutoff frequency of the first low-pass filter 208.However, no problem occurs even when the cutoff frequency of the secondlow-pass filter 209 is set to be higher than the cutoff frequency of thefirst low-pass filter 208. Further, the second low-pass filter 209 maybe omitted and the output of the second current detector 207 may bedirectly coupled to the input of the second hysteresis comparator 210.

Further, while the power supply of the first switching amplifier 206 andthe power supply of the second switching amplifier 211 are separatelyshown in the circuit diagram shown in FIG. 2, a common power may besupplied to the two switching amplifiers (inverter circuits).

Further, in the circuit diagram shown in FIG. 2, the circuit blockincluding the second hysteresis comparator 210, the second switchingamplifier 211, and the third low-pass filter 212 may be replaced by ageneral DC-DC converter. In this case, in the DC-DC converter, theoutput signal of the second low-pass filter 209 is used as a referencesignal and an output terminal of the DC-DC converter is connected to thesignal output terminal 213.

Further, using the power supply circuit 201 according to this exemplaryembodiment, a polar modulation power amplifier (high-frequency poweramplification circuit) may be formed, similar to FIG. 9. As shown inFIG. 3, for example, the high-frequency power amplification circuitaccording to this exemplary embodiment includes a signal input terminal202, a power supply circuit 201, a high-frequency modulation signalinput terminal 214, a high-frequency power amplifier 215, and ahigh-frequency modulation signal output terminal 216.

A harmonic modulation signal that is amplitude-modulated orphase-modulated is input to the high-frequency modulation signal inputterminal 214, the high-frequency power amplifier 215 amplifies thishigh-frequency modulation signal, and the amplified signal is input tothe high-frequency modulation signal output terminal 216. In this case,the signal input terminal 202 serves as an amplitude signal inputterminal and receives an amplitude signal (amplitude components) in theharmonic modulation signal input to the high-frequency modulation signalinput terminal 214. Further, the signal output terminal 213 of the powersupply circuit 201 serves as a power supply terminal and supplies apower supply generated by the power supply circuit 201 to thehigh-frequency power amplifier 215.

As described above, in this exemplary embodiment, a high linearity, awide frequency bandwidth, a large power, and a high power efficiency canbe concurrently achieved in the power supply circuit and thehigh-frequency power amplifier (high-frequency power amplificationcircuit) including the power supply circuit.

For example, as described above, in the power supply circuit 201, theoutput current of the first switching amplifier 206 is monitored and thesecond switching amplifier 211 is operated so that the output current ofthe first switching amplifier 206 becomes substantially zero in alow-frequency region. Further, the first switching amplifier is designedto decrease the parasitic capacitance and the second switching amplifier211 is designed to decrease the ON-resistance. Further, the cutofffrequency of the first low-pass filter 208 is made higher than thecutoff frequency of the third low-pass filter 212, whereby the operatingbandwidth of the first switching amplifier 206 and the operatingbandwidth of the second switching amplifier 211 are separated. Accordingto these operations, the operating bandwidth in which the firstswitching amplifier 206 and the second switching amplifier 211 aresummed up is broadened, whereby the output current of the linearamplifier 203 is reduced and the power efficiency is improved.

That is, according to this exemplary embodiment, it is possible tobroaden the frequency bandwidth of the switching amplifier withoutdecreasing the power efficiency of the switching amplifier. It istherefore possible to easily reduce the output current of the linearamplifier in which the power efficiency is poor and to improve the powerefficiency of the whole power supply circuit.

(Second Exemplary Embodiment)

Hereinafter, with reference to the drawings, a second exemplaryembodiment will be described. In this exemplary embodiment, a pluralityof (n) switching amplifiers are included in a power supply circuit.

FIG. 4 is a block diagram showing a configuration example of a powersupply circuit 301 according to this exemplary embodiment. As shown inFIG. 4, the power supply circuit 301 includes a signal input terminal302, a linear amplifier 303, n (k-th) current detectors 304-k (1≦k≦n), n(k-th) input filters 305-k (1≦k≦n), n (k-th) hysteresis comparators306-k (1≦k≦n), n (k-th) switching amplifiers 307-k (1≦k≦n), n (k-th)output filters 308-k (1≦k≦n), and a signal output terminal 309. Thesymbol n is an integer equal to or greater than two.

For example, the k-th current detector 304-k, the k-th input filter305-k, the k-th hysteresis comparator 306-k, the k-th switchingamplifier 307-k, the k-th output filter 308-k form a switching amplifierthat generates a switching amplification signal having a predeterminedfrequency band.

The signal input terminal 302 receives a signal to be amplified. Thelinear amplifier 303 amplifies the signal input through the signal inputterminal 302 and outputs the amplified signal to the signal outputterminal 309. The first current detector 304-1 detects the current valueof the signal output to the signal output terminal 309 by the linearamplifier 303 and outputs the current value.

The k-th input filter 305-k removes high-frequency components from theoutput signal of the k-th current detector 304-k and outputs theresulting signal. The k-th hysteresis comparator 306-k receives theoutput signal of the k-th input filter 305-k, determines the signallevel (high or low) of the received signal, and outputs thedetermination result. The k-th switching amplifier 307-k receives theoutput signal of the k-th hysteresis comparator 306-k, amplifies thesignal, and outputs the amplified signal.

The k-th output filter 308-k removes high-frequency components from theoutput signal of the k-th switching amplifier 307-k and outputs theresulting signal to the signal output terminal 309. The L-th (2≦≦L≦n)current detector 304-L detects the current value of the signal output tothe signal output terminal 309 by the (L−1)-th switching amplifier307-(L−1) via the (L−1)-th output filter 308-(L−1) and outputs thecurrent value. The signal output from the signal output terminal 309 isobtained by combining the output signal of the linear amplifier 303 andthe output signals of the n output filters 308-k (1≦k≦n).

Further, the k-th hysteresis comparator 306-k has a function to hold thelatest output state and has a hysteresis width (V_hys_k). When thelatest output signal is low, the output state changes to high when thevoltage of the input signal becomes equal to or greater than V_hys_k/2.In contrast, if the latest output signal is high, the output statechanges to low when the voltage of the input signal becomes equal to orlower than −V_hys_k/2.

In the aforementioned configuration, the bandwidth of the signalamplified by the (L−1)-th switching amplifier 307-(L−1) is preferablydesigned so that it is higher than the bandwidth of the signal amplifiedby the L-th switching amplifier 307-L. Specifically, the cutofffrequency of the L-th output filter 308-L is set to a frequency lowerthan the cutoff frequency of the (L−1)-th output filter 308-(L−1).However, no problem occurs even when the n output filters 308-k aredesigned in a way different from the one described above.

Since the frequency bands of the signals to be amplified by the nswitching amplifiers 307-k are different from one another, the nswitching amplifiers 307-k are preferably formed to have configurationsspecific for the respective bandwidths. For example, the L-th switchingamplifier 307-L may employ a device in which an ON-resistance is small(and a parasitic capacitance is large) compared to the (L−1)-thswitching amplifier 307-(L−1), whereby the efficiency when the L-thswitching amplifier 307-L is operated at a low speed may be improved.

By separately using the switching amplifiers as stated above, the totalfrequency bandwidth of the n switching amplifiers 307-k can be broadenedand the power loss can be suppressed. As a result, the output current ofthe linear amplifier 303 can be reduced and the power efficiency of thewhole power supply circuit 301 is improved.

While the L-th current detector 304-L is arranged between the (L−1)-thswitching amplifier 307-(L−1) and the (L−1)-th output filter 308-(L−1)in FIG. 4, the positional relation between the L-th current detector304-L and the (L−1)-th output filter 308-(L−1) may be reversed. The L-thcurrent detector 304-L is required to be provided in a stage previous tothe circuit in which the output signal of the (L−1)-th output filter308-(L−1) is combined with the output signal of the linear amplifier 303and the output signal of another output filter 308-k (k≠L−1). The roleof the L-th current detector 304-L is to detect the current output tothe signal output terminal 309 by the (L−1)-th switching amplifier307-(L−1) via the (L−1)-th output filter 308-(L−1), and may have anyconfiguration as long as this role is fulfilled.

The L-th (2≦L≦n) input filter 305-L is provided to make the frequencyband in which the L-th hysteresis comparator 306-L and the L-thswitching amplifier 307-L are operated low by removing high-frequencycomponents from the output of the L-th current detector 304-L. It istherefore desired to make the cutoff frequency of the L-th input filter305-L lower than the cutoff frequency of the (L−1)-th output filter308-(L−1). However, no problem occurs even when the cutoff frequency ofthe L-th input filter 305-L is set to be higher than the cutofffrequency of the (L−1)-th output filter 308-(L−1). Further, the k(1≦k≦n)-th input filter 305-k may be omitted and the output of the k-thcurrent detector 304-k may be directly coupled to the input of the k-thhysteresis comparator 306-k.

While the power supplies of the n switching amplifiers 307-k areseparately shown in the circuit diagram shown in FIG. 4, a common powersupply may be used.

Further, in the circuit diagram shown in FIG. 4, the circuit blockformed of the k-th hysteresis comparator 306-k, the k-th switchingamplifier 307-k, and the k-th output filter 308-k may be replaced by ageneral DC-DC converter. In this case, in the DC-DC converter, theoutput signal of the k-th input filter 305-k is used as a referencesignal and an output terminal of the DC-DC converter is connected to thesignal output terminal 309.

Further, similar to FIG. 3 of the first exemplary embodiment, a polarmodulation power amplifier (high-frequency power amplification circuit)may be formed using the power supply circuit 301 according to thisexemplary embodiment. That is, the high-frequency power amplificationcircuit according to this exemplary embodiment may include a signalinput terminal 302, a power supply circuit 301, a high-frequencymodulation signal input terminal 214, a high-frequency power amplifier215, and a high-frequency modulation signal output terminal 216, thesignal input terminal 302 may be used as an amplitude signal inputterminal, and the signal output terminal 309 may be used as a powersupply terminal.

(Third Exemplary Embodiment)

Hereinafter, with reference to the drawings, a third exemplaryembodiment will be described. In this exemplary embodiment, a powersupply circuit includes a plurality of (n) switching amplifiers, asignal conversion circuit, and a pulse signal generator.

FIG. 5 is a block diagram showing a configuration example of a powersupply circuit 401 according to this exemplary embodiment. As shown inFIG. 5, the power supply circuit 401 includes a signal input terminal402, a signal conversion circuit 403, an analog signal terminal 404, alinear amplifier 405, a high-pass filter 406, n (k-th) current detectors407-k (1≦k≦n), m (p-th) digital signal terminals 408-p (1≦p≦m), n (k-th)pulse signal generators 409-k (1≦k≦n), n (k-th) switching amplifiers410-k (1≦k≦n), n (k-th) low-pass filters 411-k (1≦k≦n), and a signaloutput terminal 412. The symbol n is an integer equal to or greater thantwo and m is an integer from 1 to n, inclusive.

For example, the k-th current detector 407-k, the k-th pulse signalgenerator 409-k, the k-th switching amplifier 410-k, and the k-thlow-pass filter 411-k form a switching amplifier that generates aswitching amplification signal having a predetermined frequency band.

The signal input terminal 402 receives a signal to be amplified. Thesignal conversion circuit 403 receives the signal from the signal inputterminal 402, performs a signal operation, and outputs an analog signalfrom the analog signal terminal 404 and one-bit pulse signal (one-bitdigital signal) from the digital signal terminal 408-p (1≦p≦m).

The linear amplifier 405 receives the signal output from the analogsignal terminal 404, amplifies the received signal, and outputs theamplified signal. The high-pass filter 406 receives the output signal ofthe linear amplifier 405, removes low-frequency signals, and outputs theresulting signal to the signal output terminal 412. The current detector407-1 detects the current value from the output signal of the high-passfilter 406 and outputs the detected value. The current detector 407-L(2≦L≦n) detects the current value from the output signal of theswitching amplifier 410-(L−1) and outputs the detected value.

The pulse signal generator 409-p (1≦p≦m) generates a one-bit pulsesignal from the output signals of the digital signal terminal 408-p andthe current detector 407-p and outputs the one-bit pulse signal. Thepulse signal generator 409-q (m+1≦q≦n) generates the one-bit pulsesignal from the output signal of the current detector 407-q and outputsthe generated signal. The switching amplifier 410-k (1≦k≦n) amplifiesthe output signal of the pulse signal generator 409-k and outputs theamplified signal. The low-pass filter 411-k removes high-frequencycomponents from the output signal of the switching amplifier 410-k andoutputs the resulting signal to the signal output terminal 412. Thesignal output from the signal output terminal 412 is obtained bycombining the output signal of the linear amplifier 405 and the outputsignals of the n low-pass filters 411-k.

In the signal conversion circuit 403, a DC offset is applied to a signaland one-bit pulse pattern is generated. The DC offset means to changethe rate of the DC voltage of the signal to be output from the signaloutput terminal 412 compared to the signal input through the signalinput terminal 402. The signal to which the DC offset is applied isconverted into one-bit signal using a one-bit ADC such as a delta-sigmaAnalog-to-Digital Converter (ADC) or a Pulse Width Modulator (PWM)circuit and the resulting signal is output from the digital signalterminal 408-p. Further, this one-bit ADC is designed to have timeconstants different from one another. In this case, the ADC that outputsthe signal to the digital signal terminal 408-p preferably has a timeconstant larger than that of the ADC that outputs the signal to thedigital signal terminal 408-(p+1) (in this example, 1≦p≦m−1). Further,by eliminating the DC offset from the signal output from the analogsignal terminal 404, the maximum value of the input/output signal of thelinear amplifier 405 may be decreased and the bias voltage of the linearamplifier 405 may be decreased. However, the aforementioned DC offset isnot essential for the exemplary embodiments of the present invention andis not preferably applied depending on the type of the signal to beamplified and the type of the load connected to the signal outputterminal 412.

Further, the circuit shown in FIG. 5 can be operated even when thehigh-pass filter 406 is omitted. However, when the high-pass filter 406is omitted, the DC offset cannot be eliminated from the signal to beoutput from the analog signal terminal 404. Such changes in the circuitconfiguration may be performed in consideration of the easiness ofimplementation, the cost, or characteristics of the signal to beamplified, for example.

The configurations of the pulse signal generator 409-p (1≦p≦m) and thepulse signal generator 409-q (m+1≦q≦n) will be described. FIGS. 6 and 7are block diagrams showing a configuration example of the pulse signalgenerator 409-p (1≦p≦m). The pulse signal generator 409-p combines theone-bit digital signal and the analog signal.

The pulse signal generator 409-p shown in FIG. 6 includes a first inputfilter 501-p, a second input filter 502-p, an analog adder 503-p, and acomparator 504-p.

The first input filter 501-p receives the output signal of the currentdetector 407-p, removes high-frequency components from the receivedsignal, and outputs the resulting signal. The second input filter 502-preceives the output signal of the digital signal terminal 408-p, removeshigh-frequency components from the received signal, and outputs theresulting signal. In this case, while the input signal of the secondinput filter 502-p is a rectangular wave, the output signal of thesecond input filter 502-p is a waveform having a finite slope such as atrapezoidal wave or a triangular wave. The analog adder 503-p receivesthe output signal of the first input filter 501-p and the output signalof the second input filter 502-p, adds the output signals, and outputsthe resulting signal. The comparator 504-p receives the output signal ofthe analog adder 503-p, outputs a high level signal when the inputsignal is positive, and outputs a low level signal when the input signalis negative. The output signal of the comparator 504-p is output to theswitching amplifier 410-p.

The pulse signal generator 409-p shown in FIG. 7 includes a first inputfilter 601-p, a second input filter 602-p, an inverting amplifier 603-p,and a comparator 604-p.

The first input filter 601-p receives the output signal of the currentdetector 407-p, removes high-frequency components from the receivedsignal, and outputs the resulting signal. The second input filter 602-preceives the output signal of the digital signal terminal 408-p, removeshigh-frequency components from the received signal, and outputs theresulting signal. In this case, while the input signal of the secondinput filter 602-p is a rectangular wave, the output signal of thesecond input filter 602-p is a waveform having a finite slope such as atrapezoidal wave or a triangular wave. The inverting amplifier 603-preceives the output signal of the first input filter 601-p, inverts thepolarity of the signal, and outputs the inverted signal. The comparator604-p receives the output signal of the second input filter 602-p andthe output signal of the inverting amplifier 603-p and outputs a highlevel signal when the output signal of the second input filter 602-p islarger than the output signal of the inverting amplifier 603-p andoutputs a low level signal when the output signal of the second inputfilter 602-p is smaller than the output signal of the invertingamplifier 603-p. The output signal of this comparator 604-p is output tothe switching amplifier 410-p.

FIG. 8 is a block diagram showing a configuration example of the pulsesignal generator 409-q (m+1≦q≦n). The pulse signal generator 409-q shownin FIG. 8 includes an input filter 701-q and a hysteresis comparator702-q.

The input filter 701-q receives the output signal of the currentdetector 407-q, removes high-frequency components from the receivedsignal, and outputs the resulting signal. The hysteresis comparator702-q receives the output signal of the input filter 701-q, determineswhether the signal level is high or low, and outputs the result of thedetermination. The output signal of the hysteresis comparator 702-q isoutput to the switching amplifier 410-q. The hysteresis comparator 702-qhas a function to hold the latest output state and has a hysteresiswidth (V_hys_q). When the latest output signal is low, the output statechanges to high when the voltage of the input signal becomes equal to orgreater than V_hys_q/2. In contrast, if the latest output signal ishigh, the output state changes to low when the voltage of the inputsignal becomes equal to or lower than −V_hys_q/2.

Further, a delay adjustment is performed on the signal output from theanalog signal terminal 404 and the signal output from the digital signalterminal 408-p in such a way that these signals have the same phase whenthey are combined by the signal output terminal 412 after beingamplified. For example, when the delay occurring in the amplificationpath of a digital signal including the pulse signal generator 409-p, theswitching amplifier 410-p, and the low-pass filter 411-p is larger thanthe delay occurring in the amplification path of an analog signalincluding the linear amplifier 405 and the high-pass filter 406, thesignal output from the analog signal terminal 404 is delayed compared tothe signal output from the digital signal terminal 408-p and the delayedsignal is output.

In the aforementioned configuration, the bandwidth of the signalamplified by the (L−1) (2≦L≦n)-th switching amplifier 410-(L−1) ispreferably designed so that it becomes higher than the bandwidth of thesignal amplified by the L-th switching amplifier 410-L. Morespecifically, the cutoff frequency of the L-th low-pass filter 411-L isset so that it becomes lower than the cutoff frequency of the (L−1)-thlow-pass filter 411-(L−1). However, no problem occurs even when the nlow-pass filters 411-k are designed in a way different from the onedescribed above.

Since the frequency bands of the signals to be amplified by the nswitching amplifiers 410-k (1≦k≦n) are different from one another, the nswitching amplifiers 410-k (1≦k≦n) are preferably formed to haveconfigurations specific for the respective bandwidths. For example, theL-th switching amplifier 410-L may employ a device in which anON-resistance is small (and a parasitic capacitance is large) comparedto the (L−1)-th switching amplifier 410-(L−1), whereby the efficiencywhen the L-th switching amplifier 410-L is operated at a low speed maybe improved.

By separately using the switching amplifiers as stated above, it ispossible to broaden the total frequency bandwidth of the n switchingamplifiers 410-k and the power loss can be suppressed. As a result, theoutput current of the linear amplifier 405 is reduced and the powerefficiency of the whole power supply circuit 401 is improved.

While the L-th current detector 407-L is arranged between the (L−1)-thswitching amplifier 410-(L−1) and the (L−1)-th low-pass filter 411-(L−1)in FIG. 5, the positional relation between the L-th current detector407-L and the (L−1)-th low-pass filter 411-(L−1) may be reversed. It isrequired, however, that the L-th current detector 407-L be provided in astage previous to the circuit in which the output signal of the (L−1)-thlow-pass filter 411-(L−1) is combined with the output signal of thelinear amplifier 405 and the output signal of another low-pass filter411-k (k≠L−1). The role of the L-th current detector 407-L is to detectthe current output to the signal output terminal 412 by the (L−1)-thswitching amplifier 410-(L−1) via the (L−1)-th low-pass filter411-(L−1), and may have any configuration as long as this role isfulfilled. The same is applicable to the high-pass filter 406 and thefirst current detector 407-1. That is, the current that flows betweenthe linear amplifier 405 and the high-pass filter 406 can be detected bythe first current detector 407-1.

In the example shown in FIG. 6 (or FIG. 7), the input filter 501-p (or601-p, 1≦p≦m) is provided to lower the frequency band in which thecomparator 504-p (or 604-p) and the p-th switching amplifier 410-poperate by removing the high-frequency components from the output of thep-th current detector 407-p. It is therefore preferable to make thecutoff frequency of the input filter 501-p (or 601-p) lower than thecutoff frequency of the (p−1)-th low-pass filter 411-(p−1). However, noproblem occurs even when the cutoff frequency of the input filter 501-p(or 601-p) is set to be higher than the cutoff frequency of the (p−1)-thlow-pass filter 411-(p−1). Further, the input filter 501-p (or 601-p)may be omitted and the output of the p-th current detector 407-p may bedirectly coupled to the input of the analog adder 503-p (or theinverting amplifier 603-p).

In the example shown in FIG. 8, the input filter 701-q (m+1≦q≦n) isprovided to make the frequency band in which the hysteresis comparator702-q and the q-th switching amplifier 410-q are operated low byremoving high-frequency components from the output of the q-th currentdetector 407-q. It is therefore preferable to make the cutoff frequencyof the input filter 701-q lower than the cutoff frequency of the(q−1)-th low-pass filter 411-(q−1). However, no problem occurs even whenthe cutoff frequency of the input filter 701-q is set to be higher thanthe cutoff frequency of the (q−1)-th low-pass filter 411-(q−1). Further,the input filter 701-q may be omitted and the output of the q-th currentdetector 407-q may be directly coupled to the input of the hysteresiscomparator 702-q.

Further, while the power supplies of the n switching amplifiers 410-k(1≦k≦n) are separately shown in the circuit diagram shown in FIG. 5, acommon power supply may be used.

Further, in the circuit diagram shown in FIG. 5, the circuit blockincluding the hysteresis comparator 702-q, the q-th switching amplifier410-q, and the q-th output filter 411-q may be replaced by a typicalDC-DC converter. In this case, in the DC-DC converter, the output signalof the input filter 701-q is used as a reference signal and the outputterminal is connected to the signal output terminal 412.

Further, similar to FIG. 3 of the first exemplary embodiment, a polarmodulation power amplifier (high-frequency power amplification circuit)may be formed using the power supply circuit 401 according to thisexemplary embodiment. That is, the high-frequency power amplificationcircuit according to this exemplary embodiment may include a signalinput terminal 402, a power supply circuit 401, a high-frequencymodulation signal input terminal 214, a high-frequency power amplifier215, and a high-frequency modulation signal output terminal 216, use thesignal input terminal 402 as an amplitude signal input terminal, and usethe signal output terminal 412 as a power supply terminal.

Note that the present invention is not limited to the aforementionedexemplary embodiments and may be changed as appropriate withoutdeparting from the spirit of the present invention.

While some or all of the aforementioned exemplary embodiments may bedescribed as shown in the following Supplementary Notes, the exemplaryembodiments are not limited to the following Supplementary Notes.

(Supplementary Note 1)

A power supply circuit comprising:

a linear amplifier that linearly amplifies a signal input from anexternal device;

a first current detector that detects a current value of a signal outputfrom the linear amplifier;

a first hysteresis comparator that receives an output signal of thefirst current detector and determines whether the signal level is highor low;

a first switching amplifier that receives an output signal of the firsthysteresis comparator and amplifies the received signal;

a first low-pass filter that removes high-frequency noise componentsfrom an output signal of the first switching amplifier and outputs theresulting signal;

a second current detector that detects current components of the outputsignal of the first switching amplifier;

a second low-pass filter that removes high-frequency noise componentsfrom an output signal of the second current detector and outputs theresulting signal;

a second hysteresis comparator that receives an output signal of thesecond low-pass filter and determines whether the signal level is highor low;

a second switching amplifier that receives an output signal of thesecond hysteresis comparator and amplifies the received signal; and

a third low-pass filter that removes high-frequency noise componentsfrom an output signal of the second switching amplifier and outputs theresulting signal,

wherein the power supply circuit combines the output signals of thelinear amplifier, the first low-pass filter, and the third low-passfilter and outputs the combined signal to an external circuit.

(Supplementary Note 2)

The power supply circuit according to Supplementary Note 1, wherein acutoff frequency of the first low-pass filter is higher than a cutofffrequency of the third low-pass filter.

(Supplementary Note 3)

The power supply circuit according to Supplementary Note 1 or 2,wherein:

the first hysteresis comparator has a function to hold the latest outputstate and has a hysteresis width (V_hys1), if the latest output signalis low, the output state changes to high when the signal level of theinput signal becomes equal to or greater than V_hys1/2, and if thelatest output signal is high, the output state changes to low when thesignal level of the input signal becomes equal to or lower than−V_hys1/2, and

the second hysteresis comparator has a function to hold the latestoutput state and has a hysteresis width (V_hys2), if the latest outputsignal is low, the output state changes to high when the signal level ofthe input signal becomes equal to or greater than V_hys2/2, and if thelatest output signal is high, the output state changes to low when thesignal level of the input signal becomes equal to or lower than−V_hys2/2.

(Supplementary Note 4)

A power supply circuit comprising:

a linear amplifier that amplifies an arbitrary input signal;

N (N is an integer equal to or greater than two) current detectors thatdetect a current value of an output signal of a switching amplifier orthe linear amplifier;

N hysteresis comparators that receive output signals of the N currentdetectors and determine the signal level (high/low) of the receivedsignal using a predetermined threshold;

N switching amplifiers that receive output signals of the N hysteresiscomparators, amplify the signals, and output the amplified signals; and

N output low-pass filters that receive output signals of the N switchingamplifiers, remove high-frequency components from the received signals,and output the resulting signals, wherein:

the first current detector detects an output current of the linearamplifier,

the L-th (L is an integer that falls within 2≦L≦N) current detectordetects an output current of the (L−1)-th switching amplifier,

the K-th (K is an integer that falls within 1≦K≦N) hysteresis comparatorreceives an output signal of the K-th current detector,

the K-th switching amplifier receives an output signal of the K-thhysteresis comparator,

the K-th output low-pass filter receives an output signal of the K-thswitching amplifier,

the K-th hysteresis comparator has a function to hold the latest outputstate and a high-side threshold (Vhigh_K) and a low-side threshold(Vlow_K), if the latest output signal is low, the output state changesto high when the voltage of the input signal becomes equal to or greaterthan Vhigh_K, and if the latest output signal is high, the output statechanges to low when the voltage of the input signal becomes equal to orlower than Vlow_K, and

the output signals of the linear amplifier and the N output low-passfilters are combined and the combined signal is output to an externalcircuit.

(Supplementary Note 5)

The power supply circuit according to Supplementary Note 4, wherein acutoff frequency of the L-th (L is an integer that falls within 2≦L≦N)output low-pass filter is lower than a cutoff frequency of the (L−1)-thoutput low-pass filter.

(Supplementary Note 6)

The power supply circuit according to Supplementary Note 4 or 5,wherein:

an input low-pass filter is provided between the K-th (K is an integerthat falls within 1≦K≦N, a plurality of values may be selected as K)current detector and the K-th hysteresis comparator, and

a signal obtained by removing high-frequency components of the outputsignal of the K-th current detector is output to the K-th hysteresiscomparator.

(Supplementary Note 7)

The power supply circuit according to Supplementary Note 6, wherein acutoff frequency of the L-th (L is an integer that falls within 2≦L≦N)input low-pass filter is lower than a cutoff frequency of the (L−1)-thoutput low-pass filter.

(Supplementary Note 8)

A power supply circuit comprising:

a signal conversion circuit that receives an arbitrary signal andgenerates one type of analog signal and M (M is an integer equal to orgreater than one) types of one-bit digital signals from the arbitrarysignal;

a linear amplifier that receives the analog signal, amplifies thereceived signal, and outputs the amplified signal;

N (N is an integer equal to or larger than two and satisfies M≦N)current detectors that detect a current value of an output signal of aswitching amplifier or the linear amplifier;

N pulse signal generators that output a rectangular signal using outputsignals of the N current detectors;

N switching amplifiers that receive output signals of the N pulse signalgenerators, amplify the received signals, and output the amplifiedsignals; and

N output low-pass filters that receive output signals of the N switchingamplifiers, remove high-frequency components from the received signals,and output the resulting signals, wherein:

the first current detector detects an output current of the linearamplifier,

the L-th (L is an integer that falls within 2≦L≦N) current detectordetects an output current of the (L−1)-th switching amplifier,

the P-th (P is an integer that falls within 1≦P≦M) pulse signalgenerator generates the rectangular signal from an output signal of theP-th current detector and the P-th one-bit digital signal,

the Q-th (Q is an integer that falls within M+1≦Q≦N) pulse signalgenerator includes a hysteresis comparator, receives the output signalof the P-th current detector, determines whether the signal level ishigh or low using a predetermined threshold, and outputs the resultingsignal as the rectangular signal,

the K-th (K is an integer that falls within 1≦K≦N) switching amplifierreceives an output signal of the K-th pulse signal generator,

the K-th (K is an integer that falls within 1≦K≦N) output low-passfilter receives an output signal of the K-th switching amplifier,

the hysteresis comparator included in the Q-th pulse signal generatorhas a function to hold the latest output state and a high-side threshold(Vhigh_Q) and a low-side threshold (Vlow_Q), if the latest output signalis low, the output state changes to high when the voltage of the inputsignal becomes equal to or greater than Vhigh_Q, and if the latestoutput signal is high, the output state changes to low when the voltageof the input signal becomes equal to or lower than Vlow_Q, and

the output signals of the linear amplifier and the N output low-passfilters are combined and the combined signal is output to an externalcircuit.

(Supplementary Note 9)

The power supply circuit according to Supplementary Note 8, wherein:

the linear amplifier comprises a high-pass filter at an output of thelinear amplifier, and

low-frequency components are removed from an output signal of the linearamplifier by the high-pass filter and then the resulting signal iscombined with the output signals of the N output low-pass filters.

(Supplementary Note 10)

The power supply circuit according to Supplementary Note 8 or 9, whereina cutoff frequency of the L-th (L is an integer that falls within 2≦L≦N)output low-pass filter is lower than a cutoff frequency of the (L−1)-thoutput low-pass filter.

(Supplementary Note 11)

The power supply circuit according to any one of Supplementary Notes 8to 10, wherein the P-th (P is an integer that falls within 1≦P≦M) pulsesignal generator comprises:

a first input low-pass filter that receives an output signal of the P-thcurrent detector, removes high-frequency components from the receivedsignal, and outputs the resulting signal;

a second input low-pass filter that receives the P-th one-bit digitalsignal and outputs a trapezoidal wave or a triangular wave obtained byremoving high-frequency components from the input signal;

an analog adder that adds an output signal of the first low-pass filterand an output signal of the second low-pass filter and outputs theresulting signal; and

a comparator that outputs a high level signal when an output signal ofthe analog adder is larger than a predetermined threshold and outputs alow level signal when the output signal of the analog adder is smallerthan the predetermined threshold, and

an output signal of the comparator is output to the P-th switchingamplifier.

(Supplementary Note 12)

The power supply circuit according to any one of Supplementary Notes 8to 10, wherein:

the P-th (P is an integer that falls within 1≦P≦M) pulse signalgenerator comprises:

-   -   a first input low-pass filter that receives an output signal of        the P-th current detector, removes high-frequency components        from the received signal, and outputs the resulting signal;    -   a second input low-pass filter that receives the P-th one-bit        digital signal and outputs a trapezoidal wave or a triangular        wave obtained by removing high-frequency components from the        input signal;    -   an inverting amplifier that receives an output signal of the        first input filter, inverts the polarity of the received signal,        and outputs the resulting signal; and    -   a comparator that receives an output signal of the second        low-pass filter and an output signal of the inverting amplifier,        outputs a high level signal when the output signal of the second        low-pass filter is larger than the output signal of the        inverting amplifier, and outputs a low level signal when the        output signal of the second low-pass filter is smaller than the        output signal of the inverting amplifier, and

an output signal of the comparator is output to the P-th switchingamplifier.

(Supplementary Note 13)

The power supply circuit according to any one of Supplementary Notes 8to 12, wherein:

an input low-pass filter is provided between the Q-th (K is an integerthat falls within M+1≦Q≦N, a plurality of values may be selected as K)current detector and the Q-th pulse signal generator, and

a signal obtained by removing high-frequency components from an outputsignal of the Q-th current detector is output to the Q-th pulse signalgenerator.

(Supplementary Note 14)

A high-frequency power amplifier comprising:

a power amplifier that amplifies a high-frequency modulation signal usedfor a desired information communication; and

the power supply circuit according to Supplementary Notes 1 to 13 thatreceives an amplitude component of the high-frequency modulation signalas an input signal,

wherein an output signal of the power supply circuit is used as a powersupply of the power amplifier.

While the present invention has been described with reference to theexemplary embodiments, the present invention is not limited to the aboveexemplary embodiments. Various changes that can be understood by thoseskilled in the art can be made to the configurations and the details ofthe present invention within the scope of the present invention.

REFERENCE SIGNS LIST

-   10 POWER SUPPLY CIRCUIT-   11 LINEAR AMPLIFIER-   12 FIRST SWITCHING AMPLIFIER-   13 SECOND SWITCHING AMPLIFIER-   14 POWER SUPPLY UNIT-   101 HIGH-FREQUENCY MODULATION SIGNAL INPUT TERMINAL-   102 AMPLITUDE SIGNAL INPUT TERMINAL-   103 POWER SUPPLY CIRCUIT-   104 HIGH-FREQUENCY POWER AMPLIFIER-   105 HIGH-FREQUENCY MODULATION SIGNAL OUTPUT TERMINAL-   106 LINEAR AMPLIFIER-   107 SUBTRACTOR-   108 CURRENT DETECTION RESISTOR-   109 HYSTERESIS COMPARATOR-   110 SWITCHING AMPLIFIER-   110 LINEAR AMPLIFIER-   111 INDUCTOR-   112 POWER SUPPLY TERMINAL-   201, 301, 401 POWER SUPPLY CIRCUIT-   202, 302, 402 SIGNAL INPUT TERMINAL-   203, 303, 405 LINEAR AMPLIFIER-   204, 207, 304-1-304-n, 407-1-407-n CURRENT DETECTOR-   205, 210, 306-1-306-n, 702-q HYSTERESIS COMPARATOR-   206, 211, 307-1-307-n, 410-1-410-n SWITCHING AMPLIFIER-   206a BUFFER CIRCUIT-   206b INVERTER CIRCUIT-   206c POWER SUPPLY-   208, 209, 212, 411-1-411-n LOW-PASS FILTER-   213, 309, 412 SIGNAL OUTPUT TERMINAL-   214 HIGH-FREQUENCY MODULATION SIGNAL INPUT TERMINAL-   215 HIGH-FREQUENCY POWER AMPLIFIER-   216 HIGH-FREQUENCY MODULATION SIGNAL OUTPUT TERMINAL-   305-1-305-n INPUT FILTER-   308-1-308-n OUTPUT FILTER-   403 SIGNAL CONVERSION CIRCUIT-   404 ANALOG SIGNAL TERMINAL-   406 HIGH-PASS FILTER-   408-1-408-m DIGITAL SIGNAL TERMINAL-   409-1-409-n PULSE SIGNAL GENERATOR-   501-p, 502-p, 601-p, 602-p, 701-q INPUT FILTER-   503-p ANALOG ADDER-   504-p, 604-p COMPARATOR-   603-p INVERTING AMPLIFIER

The invention claimed is:
 1. A power supply circuit comprising: a linearamplification unit that generates a linear amplification signal based onan input signal; a first switching amplification unit that generates afirst switching amplification signal of a first frequency band bydetecting an output signal from the linear amplification unit; a secondswitching amplification unit that generates a second switchingamplification signal of a second frequency band by detecting an outputsignal from the first switching amplification unit; and a power supplyunit that supplies a combined signal in which the linear amplificationsignal and the first and second switching amplification signals arecombined to an external circuit as a power supply.
 2. The power supplycircuit according to claim 1, wherein: the linear amplification unitlinearly amplifies the input signal and generates the linearamplification signal, the first switching amplification unit comprises:a first current detector that detects a current of the linearamplification signal and generates a first detection signal according tothe current; a first hysteresis comparator that determines the level ofthe first detection signal and generates a first determination signalaccording to the level; a first switching amplifier thatswitching-amplifies the first determination signal; and a first outputlow-pass filter that removes high-frequency components from a signalobtained by amplifying the first determination signal and generates thefirst switching amplification signal of the first frequency band, andthe second switching amplification unit comprises: a second currentdetector that detects a current of a signal obtained by amplifying thefirst determination signal and generates a second detection signalaccording to the current; a second hysteresis comparator that determinesthe level of the second detection signal and generates a seconddetermination signal according to the level; a second switchingamplifier that switching-amplifies the second determination signal; anda second output low-pass filter that removes high-frequency componentsfrom a signal obtained by amplifying the second determination signal andgenerates the second switching amplification signal of the secondfrequency band.
 3. The power supply circuit according to claim 2,wherein a cutoff frequency of the second output low-pass filter is lowerthan a cutoff frequency of the first output low-pass filter.
 4. Thepower supply circuit according to claim 2, wherein: the first switchingamplification unit comprises a first input low-pass filter that removeshigh-frequency components from the first detection signal, and the firsthysteresis comparator determines the level of a signal obtained byremoving high-frequency components from the first detection signal andgenerates the first determination signal according to the level.
 5. Thepower supply circuit according to claim 2, wherein: the second switchingamplification unit comprises a second input low-pass filter that removeshigh-frequency components from the second detection signal, and thesecond hysteresis comparator determines the level of a signal obtainedby removing high-frequency components from the second detection signaland generates the second determination signal according to the level. 6.The power supply circuit according to claim 5, wherein a cutofffrequency of the second input low-pass filter is lower than a cutofffrequency of the first output low-pass filter.
 7. A power supply circuitcomprising: a linear amplification unit that generates a linearamplification signal based on an input signal; a first switchingamplification unit that generates a first switching amplification signalof a first frequency band based on the linear amplification signal; asecond switching amplification unit that generates a second switchingamplification signal of a second frequency band based on the firstswitching amplification signal; a power supply unit that supplies acombined signal in which the linear amplification signal and the firstand second switching amplification signals are combined to an externalcircuit as a power supply; and a third switching amplification unit thatgenerates a third switching amplification signal of a third frequencyband based on the second switching amplification signal, wherein thepower supply unit combines the linear amplification signal and thefirst, the second, and the third switching amplification signals.
 8. Apower supply circuit comprising: a linear amplification unit thatgenerates a linear amplification signal based on an input signal; afirst switching amplification unit that generates a first switchingamplification signal of a first frequency band based on the linearamplification signal; a second switching amplification unit thatgenerates a second switching amplification signal of a second frequencyband based on the first switching amplification signal; a power supplyunit that supplies a combined signal in which the linear amplificationsignal and the first and second switching amplification signals arecombined to an external circuit as a power supply; and a signalconversion circuit that generates an analog signal and first and secondone-bit digital signals based on the input signal, wherein: the linearamplification unit linearly amplifies the analog signal and generatesthe linear amplification signal, the first switching amplification unitcomprises: a first current detector that detects a current of the linearamplification signal and generates a first detection signal according tothe current; a first pulse signal generator that generates a first pulsesignal based on the first detection signal and the first one-bit digitalsignal; a first switching amplifier that switching-amplifies the firstpulse signal; and a first output low-pass filter that removeshigh-frequency components from a signal obtained by amplifying the firstpulse signal and generates the first switching amplification signal ofthe first frequency band, and the second switching amplification unitcomprises: a second current detector that detects a current of a signalobtained by amplifying the first pulse signal and generates a seconddetection signal according to the current; a second pulse signalgenerator that generates a second pulse signal based on the seconddetection signal and the second one-bit digital signal; a secondswitching amplifier that switching-amplifies the second pulse signal;and a second output low-pass filter that removes high-frequencycomponents from a signal obtained by amplifying the second pulse signaland generates the second switching amplification signal of the secondfrequency band.
 9. A high-frequency power amplification circuitcomprising: a high-frequency power amplifier that amplifies ahigh-frequency modulation signal that is input; a linear amplificationunit that generates a linear amplification signal based on an amplitudesignal which is an amplitude component of the high-frequency modulationsignal; a first switching amplification unit that generates a firstswitching amplification signal of a first frequency band by detecting anoutput signal from the linear amplification unit; a second switchingamplification unit that generates a second switching amplificationsignal of a second frequency band by detecting an output signal from thefirst switching amplification unit; and a power supply unit thatsupplies a combined signal obtained by combining the linearamplification signal and the first and second switching amplificationsignals to the high-frequency power amplifier as a power supply.
 10. Apower supply control method in a power supply circuit, wherein: thepower supply circuit generates a linear amplification signal based on aninput signal, the power supply circuit generates a first switchingamplification signal of a first frequency band by detecting an outputsignal from the linear amplification unit, the power supply circuitgenerates a second switching amplification signal of a second frequencyband by detecting an output signal from the first switchingamplification unit; and the power supply circuit supplies a combinedsignal obtained by combining the linear amplification signal and thefirst and second switching amplification signals to an external circuitas a power supply.
 11. A power supply circuit comprising: a linearamplification means for generating a linear amplification signal basedon an input signal; a first switching amplification means for generatinga first switching amplification signal of a first frequency band bydetecting an output signal from the linear amplification unit; a secondswitching amplification means for generating a second switchingamplification signal of a second frequency band by detecting an outputsignal from the first switching amplification unit; and a power supplymeans for supplying a combined signal in which the linear amplificationsignal and the first and second switching amplification signals arecombined to an external circuit as a power supply.
 12. A high-frequencypower amplification circuit comprising: a high-frequency power amplifierthat amplifies a high-frequency modulation signal that is input; alinear amplification means for generating a linear amplification signalbased on an amplitude signal which is an amplitude component of thehigh-frequency modulation signal; a first switching amplification meansfor generating a first switching amplification signal of a firstfrequency band by detecting an output signal from the linearamplification unit; a second switching amplification means forgenerating a second switching amplification signal of a second frequencyband by detecting an output signal from the first switchingamplification unit; and a power supply means for supplying a combinedsignal obtained by combining the linear amplification signal and thefirst and second switching amplification signals to the high-frequencypower amplifier as a power supply.